Mud circulation systems have been used for many years in the drilling of deep wells and in that time, many leaks have developed in such systems, the leaks causing lost time and excessive costs but more importantly, the leaks sometimes causing loss of the well or the loss of life. Drilling mud is a term used for a variety of drilling fluids such as mixtures of water, oil, chemicals, clays, and any other materials that will produce desired properties such as density, viscosity, and gas penetration resistance.
Drilling mud is normally sucked from the mud tank to a battery of mud pumps where it is pressurized and pumped through a series of pipes, control devices, measuring devices, a drilling swivel, a kelley joint, down the drill string, out of the bit, up the annulus to the mud riser, through the mud return line having more measurement and control devices, through equipment to separate cuttings and back to the mud tank for reconditioning and recirculation. From the drillers position, the standpipe, hose and the drilling swivel are the only parts of the mud circulation route described above that are visible and should pressure be lost at some point along the route, valuable time passes before he realizes the loss and attempts to identify the cause and to correct the problem if it is not too late to do so. Such a loss of time worsens the results of the leak due to: the extremely abrasive qualities of most drilling muds and their ability to rapidly enlarge a leak path; the possibility of a blow out before the leak can be fixed; reduced drilling rates and premature replacement of equipment, to name a few.
The driller may have at his console a number of indicators in addition to drilling controls, such indicators showing, rate of penetration, weight on the hook, bit RPM and mud pressure, all of which usually hold his full attention as he operates the controls. It is therefore desirable that he be furnished with a method and apparatus to correlate and logic out the cause of failures from additional data such as mud pump speed, mud pump output, standpipe pressure, mud return rate and a multiplicity of pressures along the mud circulation route, as does the present invention. Hayward, in U.S. Pat. No. 2,290,179 discloses a method of signaling a predetermined percent increase in pump speed to indicate a washout but makes no attempt to correlate increased pump speed with other indicators such as changes in flow rates, or system pressures so as to prevent a signaling of washout when in fact some other failure has occurred.
McArthur, U.S. Pat. Nos. 3,895,527; 3,898,877; 4,010,642; and 4,018,088 discloses the measure of downhole pressure by use of a special tube run downhole, as does Tricon U.S. Pat. No. 3,985,027.